FIG. 1 is a conventional touch screen. The touch screen comprises a liquid crystal display (LCD) panel 100, a touch panel 150, a display controller 130 and a sensing circuit 155. In general, the touch panel 150 is fabricated on the LCD panel 100. The display controller 130 receives a video signal and converts the video signal to a panel control signal transmitted to the LCD panel 100 so that the LCD panel 100 displays the image according to the panel control signal. When one touches the touch panel 150, the touch panel 150 generates a sensing signal to the sensing circuit 155, and the sensing circuit 155 outputs a position signal according to the sensing signal.
FIG. 2A is a diagram of the LCD panel. The LCD panel 100 is generally divided into two regions—a display region 112 and a non-display region 114. The display region 112 comprises a thin film transistor (TFT) array, and the non-display region 114 comprises a gate driver 120 and a source driver 125 for controlling transistors in the TFT array. The panel control signal outputted from the display controller 130 controls the gate driver 120 to generate a gate driving signal and the source driver 125 to generate a source driving signal. The panel control signal further comprises a common voltage signal Vcom for controlling the inversion of liquid crystal in the LCD panel 100. The gate driving signal controls the TFT array to turn on or off, and the source driving signal provides brightness data for pixels. In FIG. 2A, in a portable electronic device application, the display controller 130 can be integrated with a timing controller (TCON), the gate driver 120 and the source driver 125.
The video signal comprises a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a red signal, a green signal and a blue signal. The time to display a scan line on the LCD panel 100 is a period associated with the horizontal synchronization signal Hsync, while the time to display a frame on the LCD panel 100 is a period associated with the vertical synchronization signal Vsync. That is, if the LCD panel 100 has M scan lines, the gate driver 120 can generate M gate driving signals. According to the horizontal synchronization signal Hsync, M gate driving signals can be asserted sequentially.
FIG. 2B is a diagram of the vertical synchronization signal Vsync, the horizontal synchronization signal Hsync, the common voltage signal Vcom and the gate driving signal. As shown in FIG. 2B, the period of the vertical synchronization signal Vsync begins from the start of the low level, and one period of the vertical synchronization signal Vsync comprises a plurality of periods of the horizontal synchronization signal Hsync. According to the horizontal synchronization signal Hsync, a plurality of gate driving signals are asserted sequentially, and a frequency of the common voltage signal Vcom is a half of a frequency of the horizontal synchronization signal Hsync. As mentioned above, in a portable electronic device application, the display controller 130 can be integrated with the timing controller, the gate driver 120 and the source driver 125, with the Vcom signal residing in the integrated display controller 130.
The low level interval of the vertical synchronization signal Vsync is known as a vertical blanking interval (VBI). During the VBI, the common voltage signal Vcom also remains at the low level.
FIG. 3 shows a conventional capacitive touch panel. The capacitive touch panel comprises a first sensing layer 151, a second sensing layer 152 and a shielding layer 153. Generally, the first sensing layer 151 and the second sensing layer 152 respectively comprise a plurality of capacitive sensing components. When one touches the capacitive touch panel, equivalent capacitance of the touch point is changed.
Moreover, the shielding layer 153 isolates the panel control signal from the sensing signal so that the sensing signal is not affected by noise from the panel control signal. Accordingly, the display controller 130 and the sensing circuit 155 in the conventional capacitive touch screen operate separately without communication. The conventional three-layered capacitive touch panel is much more costly than a resistive touch panel.